tunicate


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tunicate

(to͞o`nəkĭt), marine animal of the phylum ChordataChordata
, phylum of animals having a notochord, or dorsal stiffening rod, as the chief internal skeletal support at some stage of their development. Most chordates are vertebrates (animals with backbones), but the phylum also includes some small marine invertebrate animals.
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, which also includes the vertebrates. The adult form of most tunicates (also called urochordates) shows no resemblance to vertebrate animals, but such a resemblance is evident in the larva. The most familiar tunicates are the sea squirts, or ascidians (class Ascidiacea). Adult sea squirts are sedentary, filter-feeding, cylindrical or globular animals, usually found attached to rocks, shells, pilings, or boat bottoms. The soft body is surrounded by a thick test, or tunic, often transparent or translucent and varying in consistency from gelatinous to leathery. The tunic (for which the tunicates are named) is secreted by the body wall of the adult animal. It is composed of cellulose, an almost unique occurrence of that material in the animal kingdom. Two siphons project from the animal's body; water enters the incurrent siphon at the top of the body and leaves the excurrent siphon at the side. Food particles are filtered from the water by the pharynx, which occupies most of the body, and are then passed into the digestive system. Some species reproduce by budding, resulting in the formation of colonies of sea squirts, joined at their bases by slender stalks or embedded in a slab of common tunic material. In addition, nearly all species reproduce sexually and are hermaphroditic. The free-swimming larva, called a tadpole, has a muscular tail and is similar in appearance to a frog tadpole. The larva has the characteristic chordate features also found in the embryos of vertebrates: a dorsal, hollow nerve cord; a stiffening rod, or notochord; and gill slits leading into the pharynx. The tadpole eventually settles and undergoes a drastic metamorphosis into the adult form. A common solitary sea squirt of both coasts of North America is the slender, yellow, transparent Ciona intestinalis, about 2 in. (5 cm) tall. The sea peach, Tethyum pyriforme, is a round, peach-colored sea squirt found from Maine north. Sea grapes are clusters of the greenish colonial squirt, Molgula manhattensis, common from Massachusetts south. Golden stars are colonies of various Botryllus species; the bright yellow individual animals are grouped in starlike clusters in a flat, encrusting, greenish tunic. Asplidium species form colonies of minute animals embedded in a gristly tunic; chunks of such colonies, typically dead, bleached, and often washed ashore, are known as sea pork. There are two other groups of tunicates, both found in the plankton of open oceans. The salps (class Thaliacea) are barrel-shaped tunicates, open at both ends; they swim by muscular contractions that force water through the body. The related pyrosomes form free-floating, translucent and bioluminescent colonies known as sea pickles. The larvaceans (class Larvacea) retain the larval form, with a tail and a notochord, as adults. A commonly held theory maintains that vertebrates evolved from animals like the larvaceans. Larvaceans have no tunics, but secrete gelatinous containers, called houses; these are used to filter food from the water and are continuously discarded and replaced. Tunicates are classified in the phylum Chordata, subphylum Urochordata.
References in periodicals archive ?
The tunicate genome also contains clues to the source of introns, chunks of DNA that are sandwiched between protein-coding parts of genes.
Morphology and genetics of rejection reactions between oozooids from the tunicate Botryllus schlosseri.
the tunicate, Styela plicata from Sydney harbour, Australia, analysed for molecular weight of the proteins by SDS PAGE revealed that it contained a single protein of approximately 14 kDa [23].
Sea squirts are tunicates, a named derived from a firm, rubbery outer covering called a "tunic.
Collections were made again in June 2002, January and July 2003, primarily from colonies of the tunicate Eudistoma carolinense.
isolated from the surface of the tunicate Ciona intestinalis, produced at least five extra-cellular compounds that inhibited the settlement or development of a range of surface-colonizing species.
Aplidin* is a novel antitumour agent derived from the marine tunicate Aplidium albicans.
Aplidin(R) is a synthetic cyclodepsipeptide originally isolated from the marine tunicate Aplidium albicans.
Wu detected the compound using a variety of approaches, including dissecting the tunicate and filtering its cells.
Aplidin* is a cyclodepsipeptide derived from the marine tunicate Aplidium albicans.
This corollary of the lottery hypothesis is not met on Georges Bank, because encrusting bryozoans can be overgrown by the colonial tunicate Didemnum sp.
The Illinois group has manufactured didemnin B, which naturally occurs in the pancake-shaped, backbone-less tunicate, Trididemnun solidum, more commonly known as a sea squirt.